The Muscular System · PDF fileElaine N. Marieb Chapter 6 The Muscular System. ... Copyright...

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Essentials of Human Anatomy & Physiology

Seventh Edition

Elaine N. Marieb

Chapter 6

The Muscular System

Muscles are responsible for all types of body movement – they contract or shorten and are the machine of the body

Three basic muscle types are found in the body

Skeletal muscle

Cardiac muscle

Smooth muscle

Characteristics of Muscles

Muscle cells are elongated (muscle cell = muscle fiber)

Contraction of muscles is due to the movement of microfilaments

All muscles share some terminology

Prefix myo refers to muscle

Prefix mys refers to muscle

Prefix sarco refers to flesh

Skeletal Muscle Characteristics

Most are attached by tendons to bones

Cells are multinucleate

Striated – have visible banding

Voluntary – subject to conscious control

Cells are surrounded and bundled by connective tissue = great force, but tires easily

Connective Tissue Wrappings ofSkeletal Muscle

Endomysium –around single muscle fiber

Perimysium –around a fascicle (bundle) of fibers Figure 6.1

Connective Tissue Wrappings ofSkeletal Muscle

Epimysium –covers the entire skeletal muscle

Fascia – on the outside of the epimysium

Figure 6.1

Skeletal Muscle Attachments

Epimysium blends into a connective tissue attachment

Tendon – cord-like structure

Aponeuroses – sheet-like structure

Sites of muscle attachment

Cartilages

Connective tissue coverings

Smooth Muscle Characteristics

Has no striations

Spindle-shaped cells

Single nucleus

Involuntary – no conscious control

Found mainly in the walls of hollow organs

Slow, sustained and tireless Figure 6.2a

Cardiac Muscle Characteristics

Has striations

Usually has a single nucleus

Joined to another muscle cell at an intercalated disc

Involuntary

Found only in the heart

Steady pace!Figure 6.2b

Function of Muscles

Produce movement

Maintain posture

Stabilize joints

Generate heat

Properties of Skeletal Muscle Activity (single cells or fibers)

Irritability – ability to receive and respond to a stimulus

Contractility – ability to shorten when an adequate stimulus is received

Nerve Stimulus to Muscles

Skeletal muscles must be stimulated by a nerve to contract (motor neruron)

Motor unit

One neuron

Muscle cells stimulated by that neuron

Figure 6.4a

Neuromuscular junctions –association site of nerve and muscle

Figure 6.5b

Synaptic cleft –gap between nerve and muscle

Nerve and muscle do not make contact

Area between nerve and muscle is filled with interstitial fluid Figure 6.5b

Transmission of Nerve Impulse to Muscle

Neurotransmitter – chemical released by nerve upon arrival of nerve impulse

The neurotransmitter for skeletal muscle is acetylcholine

Neurotransmitter attaches to receptors on the sarcolemma

Sarcolemma becomes permeable to sodium (Na+)

Transmission of Nerve Impulse to Muscle

Sodium rushing into the cell generates an action potential

Once started, muscle contraction cannot be stopped

Contraction of a Skeletal Muscle

Muscle fiber contraction is “all or none”

Within a skeletal muscle, not all fibers may be stimulated during the same interval

Different combinations of muscle fiber contractions may give differing responses

Graded responses – different degrees of skeletal muscle shortening, rapid stimulus = constant contraction or tetanus

Muscle Response to Strong Stimuli

Muscle force depends upon the number of fibers stimulated

More fibers contracting results in greater muscle tension

Muscles can continue to contract unless they run out of energy

Energy for Muscle Contraction

Initially, muscles used stored ATP for energy

Bonds of ATP are broken to release energy

Only 4-6 seconds worth of ATP is stored by muscles

After this initial time, other pathways must be utilized to produce ATP

Direct phosphorylation

Muscle cells contain creatine phosphate (CP)

CP is a high-energy molecule

After ATP is depleted, ADP is left

CP transfers energy to ADP, to regenerate ATP

CP supplies are exhausted in about 20 seconds

Figure 6.10a

Anaerobic glycolysis

Reaction that breaks down glucose without oxygen

Glucose is broken down to pyruvic acid to produce some ATP

Pyruvic acid is converted to lactic acid

Figure 6.10b

Anaerobic glycolysis (continued)

This reaction is not as efficient, but is fast

Huge amounts of glucose are needed

Lactic acid produces muscle fatigue

Figure 6.10b

Aerobic Respiration

Series of metabolic pathways that occur in the mitochondria

Glucose is broken down to carbon dioxide and water, releasing energy

This is a slower reaction that requires continuous oxygen

Figure 6.10c

Muscle Fatigue and Oxygen Debt

When a muscle is fatigued, it is unable to contract

The common reason for muscle fatigue is oxygen debt

Oxygen must be “repaid” to tissue to remove oxygen debt

Oxygen is required to get rid of accumulated lactic acid

Increasing acidity (from lactic acid) and lack of ATP causes the muscle to contract less

Types of Muscle Contractions

Isotonic contractions

Myofilaments are able to slide past each other during contractions

The muscle shortens

Isometric contractions

Tension in the muscles increases

The muscle is unable to shorten

Muscle Tone

Some fibers are contracted even in a relaxed muscle

Different fibers contract at different times to provide muscle tone

The process of stimulating various fibers is under involuntary control

Muscles and Body Movements

Movement is attained due to a muscle moving an attached bone

Figure 6.12

Muscles and Body Movements

Muscles are attached to at least two points

Origin –attachment to a immoveable bone

Insertion –attachment to an movable bone

Figure 6.12

Effects of Exercise on Muscle

Results of increased muscle use

Increase in muscle size

Increase in muscle strength

Increase in muscle efficiency

Muscle becomes more fatigue resistant

Types of Ordinary Body

Movements

Flexion – decreases angle of joint and brings two bones closer together

Extension- opposite of flexion

Rotation- movement of a bone in longitudinal axis, shaking head “no”

Abduction/Adduction (see slides)

Circumduction (see slides)

Body Movements

Figure 6.13

Abduction –

moving the

leg away

from the

midline

Above –

Adduction-

moving

toward the

midline

Right:

Circumduction: cone-

shaped movement,

proximal end doesn’t

move, while distal end

moves in a circle.

Types of Muscles

Prime mover – muscle with the major responsibility for a certain movement

Antagonist – muscle that opposes or reverses a prime mover

Synergist – muscle that aids a prime mover in a movement and helps prevent rotation

Naming of Skeletal Muscles

Direction of muscle fibers

Example: rectus (straight)

Relative size of the muscle

Example: maximus (largest)

Location of the muscle

Example: many muscles are named for bones (e.g., temporalis)

Number of origins

Example: triceps (three heads)

Location of the muscles origin and insertion

Example: sterno (on the sternum)

Shape of the muscle

Example: deltoid (triangular)

Action of the muscle

Example: flexor and extensor (flexes or extends a bone)

Head and Neck Muscles

Figure 6.14

Trunk Muscles

Figure 6.15

Deep Trunk and Arm Muscles

Figure 6.16

Muscles of the Pelvis, Hip, and Thigh

Figure 6.18c

Muscles of the Lower Leg

Figure 6.19

Superficial Muscles: Anterior

Figure 6.20

Superficial Muscles: Posterior

Figure 6.21

The Muscular System · PDF fileElaine N. Marieb Chapter 6 The Muscular System. ... Copyright...

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